Just unpack an existing epub and reuse those files and simply change the content, and keep those files for new titles.

Thanks for that, Adjust. That's exactly what I'm doing already. It just becomes very tedious (especially with the OPF). And it's too easy to make a mistake. I'm not a programmer, but I would have thought it would be relatively simple to build an applet which would scan the unzipped project files and generate an OPF. The NCX of course would need to be to generated first and would need some user input to determine play order.